Zoom Extension API (chrome)

chrome/browser/ui/zoom/zoom_event_manager.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_ZOOM_ZOOM_EVENT_MANAGER_H_
+#define CHROME_BROWSER_UI_ZOOM_ZOOM_EVENT_MANAGER_H_
+
+#include "base/callback_list.h"
+#include "base/supports_user_data.h"
+#include "content/public/browser/host_zoom_map.h"
+
+namespace content {
+class BrowserContext;
+}  // namespace content
+
+class ZoomEventManager : public base::SupportsUserData::Data {

[Devlin, 2014/06/19 21:15:30]

This whole class seems a little odd to me.  Is this just to marshal all the
OnZoomLevelChanged() into a per-browser-context interface?  Is there any (good)
way of just having the subscribers to this class observe ZoomController
directly?

[wjmaclean, 2014/06/20 22:01:34]

The observers for this are per-browser-context as you note, and so is this.
ZoomControllers come and go with each WebContents. The observers would need to
be notified every time a new ZoomController was created, so I think this makes
more sense.

+ public:
+  static ZoomEventManager* GetForBrowserContext(
+      content::BrowserContext* context);
+
+  ZoomEventManager();
+  virtual ~ZoomEventManager();
+
+  // Called by ZoomControllers when changes are made to zoom levels in manual
+  // mode in order that browser listeners can be notified.
+  void OnZoomLevelChanged(const content::HostZoomMap::ZoomLevelChange& change);
+
+  // Add and remove zoom level changed callbacks.
+  scoped_ptr<content::HostZoomMap::Subscription> AddZoomLevelChangedCallback(
+      const content::HostZoomMap::ZoomLevelChangedCallback& callback);
+
+ private:
+  base::CallbackList<void(const content::HostZoomMap::ZoomLevelChange&)>
+      zoom_level_changed_callbacks_;
+};

[Devlin, 2014/06/19 21:15:30]

nit: newline here

[wjmaclean, 2014/06/20 22:01:34]

Done.

+#endif  // CHROME_BROWSER_UI_ZOOM_ZOOM_EVENT_MANAGER_H_